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(CNN)When an "overheated and dehydrated" Hillary Clinton stumbled into a van as she left a 9/11 memorial ceremony on Sunday morning, conspiracy theorists rejoiced.

A few hours later, after it was revealed she had come down with pneumonia -- a common illness now being treated with antibiotics and a few days' rest -- they got back to work, retrofitting baseless and lurid suggestions about her health.

The weekend wobble was treated by some political rivals and online antagonists as validation -- proof positive that the Democratic nominee was unfit, in the most literal terms, for the presidency.

A shadow campaign pushing rumors that Clinton is hiding a grave illness to protect her White House aspirations has existed for years, but only found a voice and high-profile champions during the last few months of this general election contest.

Even as Clinton took a brief leave from the stump -- she is set to resume travelon Thursday -- her campaign wrestled with legitimate questions about a lack of transparency during the Sunday scare, the rumor mill churned apace.

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Donald Trump, who has considerably been less open about his health, was mostly restrained in the aftermath -- though he did couch his well wishes with some goading analysis, saying on Monday: "I just see what I see -- the coughing fit was a week ago, so I assume that was pneumonia also."

Or not. Facts have rarely gotten in the way of dubious suggestions about Clinton's health. In a letter released Wednesday, her physician made a point of stating that the candidate "is in excellent mental condition."

Here -- quite apart from any legitimate concern stemming from her recent illness -- are a few of the more ludicrous and resilient theories:

Whatever might be wrong, it's now being covered up by ... a body double!

In the aftermath of the Sunday incident, web sleuths turned up a series of images they believe show the Clinton campaign used a "body double" to reassure the public and trick the press. Collected under the hashtag, #HillarysBodyDouble, photographs of the candidate before and after she fell ill are being compared, as features like her nose, ears and fingers are plotted side-by-side for examination and debate.

"Shocking claims are coming forward about a body double and who really emerged from (daughter) Chelsea's apartment [on Sunday]," blared the right wing Madworldnews.com.

Clinton is sick ... because someone, perhaps a Russian agent, is poisoning her

Dr. Bennet Omalu, the forensic pathologist whose role in highlighting the aftereffects of head trauma on former NFL players was dramatized by Will Smith in a recent film, weighed in with his own theory on Sunday night.

"I must advice (sic) the Clinton campaign to perform toxicologic analysis of Ms. Clinton's blood," he tweeted. "It is possible she is being poisoned."

I must advice the Clinton campaign to perform toxicologic analysis of Ms. Clinton's blood. It is possible she is being poisoned.

Omalu is, on the face of it, a more credible source and discerning eye, but, though a doctor, he has not examined Clinton. Rather than expand on his medical reasoning, he followed up a little less than an hour later with a cryptic tweet: "I do not trust Mr. Putin and Mr. Trump. With those two all things are possible."

I do not trust Mr. Putin and Mr. Trump. With those two all things are possible.

Though Putin's government has been implicated in the 2006 poisoning death of a former KGB operative in London, there is no evidence -- and nothing in any of Clinton's medical notices, provided by her physician -- to suggest anything of the sort is at play here.

Multiple currently circulating theories attach themselves to the 2012 fall, including one pushed by Trump spokesperson Katrina Pierson, who in August offered matter-of-factly that Clinton was suffering from dysphasia, a neurological disorder that complicates speech and language comprehension due to brain trauma or disease.

"What's new are the other reports of the observations of Hillary Clinton's behavior and mannerisms," Pierson said during an appearance on MSNBC, after being asked why the campaign was indulging the rumors. "Specifically with what you just showed in those previous clips, as well as her dysphasia, the fact that she's fallen, she has had a concussion."

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Meanwhile, a Fox News contributor Dr. Marc Siegel -- who himself has noted that he is "not a neurologist" -- pushed a similar line.

"I saw the same video you saw, and I'm wondering about a word called 'aphasia,' where you're searching for words, you suddenly lose those words, and that can be the sign, again, of some kind of traumatic brain injury or the after-effects of a concussion," he said on pro-Trump commentator Sean Hannity's show.

Brain damage, seizures, Alzheimer's and Parkinson's disease

The list of purported maladies goes on.

Karl Rove, the former top adviser to President George W. Bush, suggested in 2014 Clinton had been "wearing glasses that are only for people who have traumatic brain injury," while assorted right-wing sites and Twitter trolls have suggested she is prone to seizures -- a belief that sprung a new theory claiming a Secret Service agent's flashlight was really an "an auto-injector with Diazepam."

The conservative Powerline blog featured an anonymous letter on Sunday, from who it described as a "prominent internist," suggesting Clinton's pneumonia was related to Parkinson's:

"I raise this second possibility," he wrote, "because of Hillary's history of neurological illnesses (blood clot in brain, concussion), hints raised on the internet in Wikileaks documents and by others that she may have a neurological disease like Parkinson's, and her by now well documented history of recurrent coughing fits. This second possibility is that she has an aspiration pneumonia."

The first possibility, stated at the top, was that she simply had contracted the illness, like any other "healthy person living her usual life."